1. Field of the Invention
The present invention is related to the method and system for simultaneous control of the throttle valve and fuel injection to ensure that the torque and air fuel ratio of the automobile engine will reach target values.
2. DESCRIPTION OF THE PRIOR ART
A method to control the throttle valve and fuel injection to ensure that both torque and air fuel ratio of the automobile engine will reach target values is described in the Japanese Patent Application Laid-open NO.60-175742. According to this method, the angle through which the throttle is moved .DELTA..theta. is calculated by searching a prearranged table on the basis of the difference (Z-T) between the target torque Z calculated using the proper torque function and actual torque T. Or angle through which the throttle is moved amount .DELTA..theta. is calculated by PID control according to the said difference. Furthermore, the throttle valve actuator is supplied with a drive signal which changes the throttle angle by a calculated throttle angle angle .DELTA..theta..
All prior methods utilize feedback control to allow the target value to reach the actual value. When feedback control is used, overshooting tends to occur in the controlled variable when an attempt is made to improve the control response, whereas the tracking performance of the controlled variable to the target value deteriorates when an attempt is made to stabilize the system to eliminate the possibility of overshooting. In either case, the torque which is a controlled variable cannot be controlled to the target value with a high precision. Namely, such prior methods are accompanied by the problem that the engine generated torque cannot be maintained at a proper value within a variety of operating ranges. Another problem is that, since said methods also use a torque sensor, the cost is increased by the price of the sensor.